This application claims the priority of German application 198 20 534.1, filed May 8, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for adjusting the relative rotational position of camshafts that are rotatably supported and operable for actuating valves in an internal combustion engine.
European Patent Document EP 0 445 356 B1 relates to a device for adjusting the relative rotational positions of two camshafts located in a cylinder head of an internal combustion engine. The adjustment processes produce a change in the valve control times. This device has proven itself in practice, especially because, in addition to the teleological influence on the control times of the internal combustion engine, it is easy to integrate into a secondary chain drive and its components are simple and function well. (See reprint from ATZ Automobiltechnische Zeitschrift 93 (1991), Volume 10 and MTZ Motortechnische Zeitschrift (52) 1991, No. 12.
A comparable device is found in German Patent Document DE 40 41 785 A1 which can likewise be used in a chain drive between two camshafts.
Both devices comprise pistons inserted into one another and operating hydraulically, with zero pressure when the engine is at rest. When the engine is started, therefore, as a result of the load imposed by one piston through the tight side of the chain, an adjusting force is exerted on the adjusting mechanism, against the advance or retard stop, that produces metallic noises in the device.
A goal of the invention therefore is to make provisions in devices of the above general type that prevent an undesired adjusting process when the engine starts.
This goal is achieved according to the invention by providing an arrangement, wherein said device cooperates with a locking device that secures the positioning mechanism of the hydraulic piston of the device before starting or up to a point shortly after the starting of the engine.
Additional features that characterize preferred embodiments of the invention are described below and in the claims that follow.
Primary advantages achieved with the preferred embodiments of the invention arise from the fact that the locking device acts on the adjusting mechanism of the device during starting, especially during a cold start, of the engine, in such fashion that adjustment of the device is prevented. As a result, assurance is provided that the device remains in a specified basic position for up to 3 seconds following the starting process or the starting of the engine. As a result, undesirable noises produced at the stops by the outer hydraulic piston are prevented when the system, still at zero pressure, attempts to move this outer hydraulic piston from a first end position into a second end position by means of the tight side of the chain. As soon as the hydraulic pressure has built up, the locking piston of the locking device is unlocked and the adjusting mechanism and/or outer hydraulic piston operates in accordance with the specified switching points, in other words as a function of the engine parameters rpm and load which is equivalent to accelerator position.
The arrangement and design of the locking piston is simple, which not only ensures proper functioning of the locking device but also means that the parts can be easily manufactured. In addition, the reliable cooperation of the locking piston with the spring element and the hydraulic medium should be emphasized, as well as the compact design.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.